[ppi] [ppiindia] Mud volcano floods Java

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http://www.nature.com/news/2006/060828/full/060828-1.html

Published online: 29 August 2006; Corrected online: 30 August 2006 | 
doi:10.1038/news060828-1 
Mud volcano floods Java
Disaster-plagued Indonesian island faces new threat. 
Richard Van Noorden

     
     
     
What has happened?



           
            Residents carry their belongings through mud as they evacuate their 
homes in east Java.

            TRISNADI/AP/EMPICS 
     
For 3 months a sea of hot mud has been gushing from the ground in Sidoarjo, 
East Java, 35 kilometres south of Indonesia's second largest city, Surabaya. 
The steaming mud pool is growing at an estimated 50,000 cubic metres a day, 
accompanied by hydrogen sulphide gas, and now reportedly covers more than 25 
square kilometres. The flow has not yet been stopped; thousands of people have 
lost their homes.

How bizarre... has this sort of disaster happened before?

The Sidoarjo disaster is an example of a 'mud volcano'. Mud and gas accumulates 
when sea sediments are trapped in subduction zones, where one tectonic plate 
slides under another, and can erupt out of volcanic cones or simply from a 
crack in the ground. Mud volcanoes have burst on every continent, but are 
abundant in the South Caspian region (offshore and onshore Azerbaijan) and 
offshore Indonesia in the East Java Basin.

But the Sidoarjo mud volcano is rather unusual. It's huge. And, says Sam Rice, 
a geologist at the University of Cambridge, UK, reports of the mud eruption 
suggest that it is a hybrid between typical mud volcanoes and hydrothermal 
vents. The mud is of an unusually high temperature (60 °C) and contains 
enormously high concentrations of hydrogen sulphide gas. This suggests that 
some kind of volcanic, hydrothermal activity is going on at the same time.

What creates the conditions for a mud volcano?

Achim Kopf, a geologist from the University of Bremen, Germany, who has studied 
mud volcanoes extensively, explains that marine sediment can be scraped off an 
oceanic tectonic plate as it slides underneath a continental plate. If the 
sediment accumulates rapidly and water is trapped in its pores, this can stop 
the sediment being cemented by pressure. The resulting reservoir of mud can be 
trapped underground. In the case of the East Java mud flow, the mud is thought 
to have come from a reservoir some 2.7 kilometres below the Earth's surface.

And what triggers an eruption?

A number of things can create a crack that allows trapped mud to bubble to the 
surface; particularly earthquakes and drilling.

And in Java specifically?

In Java both of these things have happened recently. The oil and gas 
exploration company PT Lapindo Brantas is drilling in the area, and the gas and 
hot mud first spewed from the company's drilling rig on 28 May.

Geologist Georg Delisle of the Federal Institute for Geosciences and Natural 
Resources (BGR), Hannover, Germany, explains that the drilling apparently 
penetrated into the liquid sediment and created a connection back to the 
surface. The pressure then squeezed up the mud, like toothpaste from a tube. 
But it is likely that other connections were made to the surface, he adds - not 
just through the drilling pipe - because attempts to pump concrete into the 
pipe to block the flow of mud have failed. 

On 27 May an earthquake struck and devastated Yogyakarta on Java, and this too 
could have cracked the ground, potentially helping to release the mud. But the 
quake's epicentre was some 300 kilometres away from the mud volcano (making it 
only 2 on the Richter scale in that area).

The issue of what, exactly, caused this disaster is highly politically charged. 
It is still under investigation by police, the government and international 
experts.

Just how big is the eruption?

According to many geological experts, the scale of this mud volcano is 
unprecedented - at least on land. 

In 1945, the Makran earthquake in Pakistan triggered the sudden emergence of 
three offshore mud volcanoes, and in March 1999 a mud volcano rose out of the 
water overnight to form Malan Island, 3 kilometres from Pakistan's coast. It is 
hard to estimate the volume of mud created by such underwater eruptions. And, 
notes Rice: "Because the extrusion of mud and toxic gas occurs on the seabed it 
does not threaten human life and does not make the headlines."

'Well-kick' - the sudden surface eruption of gas and mud during offshore oil 
drilling - is common, but usually stops after a few days. Delisle recalls a 
smaller-scale incident in the 1960s where a geothermal well in the Wairakei 
geothermal field, New Zealand, ran wild: it took 3 months to stop the 
geothermal steam that found its way to the surface alongside the original 
borehole.

Can the disaster be stopped?

Nobody knows. So far, nothing has worked. PT Lapindo Brantas's senior 
vice-president Imam Agustino has been quoted saying: "The best-case scenario 
[for stopping the mudflow] is now mid-November, but I have to admit it might 
never be stopped."

Visit our newsblog to read and post comments about this story.

* This article originally stated that Sam Rice was a geologist with the 
Cambridge Antarctic Shelf Programme; he is with CASP, which previously stood 
for the Cambridge 'Arctic' Shelf Programme. 


     


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